1. Field of the Invention
The present invention relates to a manufacturing method of urethane foam molded products used, for example, on vehicle seat cushions, furniture, beds and other cushions, and more particularly to a manufacturing method of urethane foam molded products suitable for manufacturing molded products of cold cure-type urethane foams.
2. Description of the Related Art
Molded products of urethane foam used in automobile seats or the like are formed in a desired shape by injecting the raw liquid of urethane foam into a mold kept at a specific temperature, foaming and curing.
Hitherto, in manufacturing molded products of cold cure-type urethane foam cured around 60.degree. C., wax such as polyethylene was used as a releasing agent. As compared with hot cure-type urethane form cured around 100.degree. C., the cold cure-type urethane foam is low in its treating temperature, and therefore migration of releasing agent onto the surface of the urethane foam molded product is less, even in the case of wax with a relatively low melting point.
In the conventional wax in paste form, however, when urethane foam is molded, the surface of the agent on the internal surface of the mold is disturbed. When the agent is repeatedly applied on the mold, therefore, much wax is unevenly accumulated on the internal surface of the mold, and the asperities of the agent on the mold internal surface become significant. When manufactured by using such mold, the surface of the molded product of the urethane foam becomes very poor.
Besides, the releasing agent migrates, although very slightly, onto the surface of the molded product of urethane foam. Even a slight amount may cause induction of an unusual noise depending on the application of the urethane foam molded product. For example, in the case of the urethane foam molded product used in an automobile seat cushion when the urethane foam molded product is contacted with a metallic frame, if the agent is left over on the molded product, an unusual noise may be caused when the molded product rubs against the metallic frame.
To solve this problem, it has been proposed to use organopolysiloxane (hereinafter called also silicone) as a releasing agent. The silicone agent is, like the conventional releasing agent, applied on the internal surface of the mold, and cured, and the urethane foam raw liquid is injected into the mold, foamed and cured.
Generally, the silicone agent hardly migrates onto the surface of the urethane foam molded product, and when the application of releasing agent is repeated, the agent is likely to accumulate on the internal surface of the mold. Accordingly, all silicone releasing agents are not always suited to the manufacture of urethane foam molded products. For example, practical prior art processes are disclosed in the U.S. Pat. Nos. 4,244,912, 4,681,714, 4,769,204, and 4,220,727.
If a silicone releasing agent which cannot be applied uniformly on the internal surface of the mold is used, the thickness of the agent on the internal surface of the mold is uneven or a part of the agent may be locally separated from the internal surface of the mold. Therefore, every time the application of releasing agent is repeated, the agent is accumulated unevenly on the internal surface of the mold, and asperities exceeding the allowable limit may be produced shortly on the internal surface of the mold.
Still more, since the treating temperature of cold cure-type urethane foam is as low as around 60.degree. C., in the conventional silicone releasing agent, the curing was very slow and it was not suited to practical use. If the urethane foam is molded, while a part of the releasing agent is stuck uncured on the internal surface of the mold, the surface of the molded product of urethane foam is very rough, and the value as a product is lost.